The Rotating Detonation Mechanism Of Tangential Combustion Instability In A Liquid Rocket Engine

As one of the most serious problems in the development of liquid rocket engine,combustion instabilities are the focus worldwide.Although characteristics of tangential instability were obtained with a lot of works,the inner inducing mechanism has not been understood yet because the various possibility.Rotating detonation may be one of the causations inducing the tangential combustion instability in liquid rocket engine.Using combination of experimental ovservation and numerical simulation,the flow-field structure and rotating characteristics of the rotating detonation wave in both annular and hollow combustor chambers have been studied in the present paper.Firstly,to get the effects of chamber width on the hydrogen/air rotating detonation,three-dimensional models with different chamber width have been investigated.By using a one-step chemical reaction model,one wave is induced in all models.The chamber width has a significant effect on the flow field.When the chamber width is small,the variation of the flow flied with the radius is not obvious.But when the width increases,wave reflected between the inner and outer walls at the head until disappeared.With the increase of chamber width,the curvature of the wave become enlarged.The propagation velocities on the outer wall in all geometry are larger than the CJ value while the velocities on the inner wall are smaller than the CJ value.When the width between the outer and inner walls is large,this phenomenon becomes more evident.The normal velocities on the outer wall are approximate the CJ value.H₂/Air rotating detonation are experimentally achieved in a hollow chamber by decreasing the length of inner cylinder gradually.Continuous rotating detonation（CRD）patterns in both two types of chambers are presented.Two-peak phenomenon appears in the annular chamber,but it doesn’t exist in the hollow chamber.The detonation in the vicinity of the wall of the hollow chamber is over-driven.The propagation stability of different patterns has been discussed.The results show that one-wave detonation is a stable mode.The low limit equivalence ratios（ER）of detonation in the hollow chamber is smaller than that in the annular chamber.It is easier to establish rotating detonation in the hollow chamber.H₂/Air rotating detonations are experimentally achieved in a hollow chamber with a Laval nozzle.Continuous rotating detonation（CRD）pattern in three different types are presented.A new type of detonation is defined as two dominant peaks over-driven（TDPO）one wave mode based on its character.The pattern of rotating detonation relates to the reflected wave.The results verify the possibility of rotating detonation in the hollow chamber with a nozzle.To investigate the inner mechanism of the rotating detonation and tangential instability,two different ignition methods,named hot-jet and spark-plug respectively,are adopt to compare the tangential instability and rotating detonation.The results show that the realization of rotating detonation by spark-plug is impossible when the contraction ratio of the nozzle is small.When the contraction ratio is 10 and 12,the intrinsic frequencies of the test mode have been computed.The statistic results show that the dominant frequencies of experimental results are close to the intrinsic frequencies of the test mode.The error is within 5%.Besides the effects of chamber length and propellant have been investigated.At last,the possibility of rotating detonation in a hollow chamber whose center filled with injectors have been verified.The research results will enrich the theories of rotating detonation and liquid rocket engine combustion instability,and provide theoretical guidance and technical support for rocket engine combustion instability restrain.